The invention relates to a system and method to operate an internal combustion engine to facilitate the operation of secondary devices, such as emission aftertreatment devices, which depend on the operating condition of the engine to which they are coupled. In the present invention, the internal combustion engine is part of a hybrid vehicle system.
The primary function of an automobile is to transport passengers and cargo. There are, however, secondary vehicular functions including cooling the vehicle cabin, heating the vehicle cabin, and exhaust aftertreatment functions to lower the emission of regulated gaseous components from the vehicle which are performed as well. In a conventional vehicle, the operating condition of the engine must be selected to provide the torque demanded by the operator. The secondary functions are typically attended to by operating the engine at a condition which provides the desired power but may be less than a desirable operating condition from the standpoint of providing the best function of the engine dependent auxiliary device, i.e., the device which provides the secondary function. Several examples of the problems encountered in providing secondary functions in conventional vehicles follow.
If the temperature in a vehicle cabin increases above a set point of an air-conditioner thermostat, engine power is increased to provide power to drive the air conditioning compressor, while desired power at the wheels, i.e., the primary function. Increasing the power level of the engine is inefficient at many operating conditions. Clearly, it would not be satisfactory to the operator of the vehicle to delay air conditioning until the engine happened to be at a desirable condition to facilitate efficient employment of the air conditioner. Thus, in a conventional vehicle, the engine power is raised and a large fuel penalty may result.
A diesel engine equipped with a diesel particulate filter requires periodic regeneration of the filter to avoid complete occlusion of the filter. There are engine operating conditions which could cause the carbonaceous material collected in the filter to spontaneously ignite and oxidize. However, the filter must be regenerated at the time that it has become full, regardless of the current engine operating condition. Prior art approaches include electrically heating the particulate filter to the auto ignition temperature of the particulate matter, providing a burner in the exhaust system to ignite the particulate matter, operating the engine at a retarded injection timing or with exhaust gas recirculation (EGR) to cause the exhaust temperature to rise, and others. However, all prior art methods penalize fuel efficiency and many of them do not guarantee regeneration success over all possible operating scenarios.
A further example of a problem in operating a secondary device occurs in diesel-equipped conventional vehicles in which cabin heating is notably slow. Measures may be undertaken to cabin warm up. However, these measures negatively impact fuel economy and are insufficient to provide the desired cabin comfort to the operator. Thus, heating of the cabin may be delayed until an engine operating condition is accessed which can satisfy both the primary function, i.e., power at the driving wheels, and the secondary function, heating the cabin.
Yet another example of a challenge in providing a secondary function in a vehicle is in managing lean NOx traps (LNTs) for exhaust aftertreatment of homogeneous charge (fuel and air premixed) and stratified charge (fuel and air separated) lean bum engine exhaust. LNTs collect NOx during lean operation of the engine and subsequently release and react the NOx during a period of rich operation. One of the difficulties encountered in conventional vehicles utilizing an LNT is in maintaining smooth torque in making transitions between lean and rich operation to purge the LNT of NOx.
The inventors of the present invention have recognized a method to operate a hybrid vehicle system, i.e., one with an internal combustion engine and another machine which may provide motive force to the wheels, in such a manner to satisfy or attend to demands of engine dependent auxiliary devices to better provide secondary functions, such as emission control, cabin heating, and cabin cooling.